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A calibration protocol was established for a quartz microbalance-based electronic nose (QMBE-nose) that was used for apple aroma measurements. A gas-mixing panel was built to generate a broad concentration range of single apple volatile compounds and of mixtures of two compounds. The response of each QMB sensor was modelled with BET adsorption isotherms. Results show that the affinity of the different sensors to relative humidity can be described well with the BET parameters. The sensors could also be characterised with this model for affinity towards single apple volatiles and mixtures of two apple volatile compounds. By means of multivariate analysis on all sensor responses, the different compounds could be discriminated well and also quantified accurately. The results showed the potential of the QMBE-nose to quantify and discriminate different apple volatile compounds. Also, the established calibration protocol offers an easy and fast tool to characterise new sensors or investigate new application possibilities.

The performance of a quartz microbalance based electronic nose (E-nose) and a mass spectrometry based electronic nose (MSE-nose) for tomato aroma profiling has been evaluated. Solid phase micro-extraction (SPME) headspace sampling combined with gas chromatography (GC) has been used as a reference method. In the first experiment, the changes in tomato aroma profiles of two different cultivars have been monitored during shelf life (Days 1, 8, 12 and 19). The score plot of the principal component analysis (PCA) for the E-nose measurements shows a slight shift along the first principal component corresponding to an increasing number of days of shelf life. However, the tomato aroma profiles measured on Days 1 and 8 could not be discriminated by the E-nose. In contrast, MSE-nose score plots indicated an evident change in aroma profile with shelf life. The loading plots of the PCA reveals that mainly three discriminant mass to charge ratios ( m/z = 93, 43 and 57) are responsible of the observed shelf life effect in both cultivars. These fragments indicate that β-phellandrene, 6-methyl-5-hepten-2-one, 1-nitropentane and 2-methylbutanol undergo important concentration changes during shelf life of tomatoes. In the second experiment, the aroma differences between cultivars were analysed by means of the electronic nose systems. A clear distinction between cultivars based on MSE-nose measurements is obtained; however, based on E-nose measurements it is difficult to discriminate between tomato varieties in two dimensions.